The present invention relates generally to the manufacture of printed circuit boards and, more specifically, to a method for forming a folded rigid circuit board.
Space constraints are a significant burden in the designing of electronic modules. Electronic circuit designers have a continual need to provide an increasing amount of circuitry in a smaller amount of space.
One way to reduce the package size of a module is to mount portions of the circuit opposite each other within the module. Mounting a circuit board in this manner may be accomplished in several ways.
One way to construct such a module is to manufacture the circuit traces on a flexible film such as a polyimide film or polyester substrate film. The film is bent to fit within the module. Such films, however, have a relatively high cost and are not well suited for high temperature processing techniques desirable for high volume production. Another drawback is that circuit traces are limited to a single thickness making the routing of such traces difficult in intricate circuit designs.
Another technique is to manufacture two separate rigid circuit boards and inter connect them with a flexible film portion. One drawback to this configuration is that connectors must be provided at the rigid/flexible circuit board interface. Another drawback is that circuit traces in the flexible portion are limited to a single thickness. Yet another drawback to such a system is that the circuit boards typically are manufactured in one location and populated in another location. The circuit boards are populated in separate locations and must then both be relocated to a further location to be interconnected in the module, thereby adding to the complexity of the manufacturing process.
Another packaging technique is to bend a circuit board as described in U.S. Pat. No. 3,255,299. In this patent, a circuit board having one conductive layer is cut thinly in one region and bent only ninety degrees. The circuit board is cut so thin that the board becomes flexible. Such a circuit board is not adapted to unbending or rebending. These would result in separating the conductor from the substrate. Unbending is a desirable feature since circuit boards are commonly reworked to cure defects. The design shown in this patent is also limited to one layer of conductive material in the thinly cut area.
It would therefore be desirable to have a circuit board with multilayers of traces capable of flexing in a region capable of repeated bending.